Power transistors, in particular insulated-gate bipolar transistors (IGBTs) are often used in energy, forming and transmission technology for the purpose of fast and low-loss switching of currents. To be able to switch high currents (in particular in the order of magnitude of 1 kA and above), a multiplicity of individual power semiconductor components, also referred to in the following text as power transistors, are electrically connected in parallel here. In this case, the power transistors are often combined in modules, which, among other things, makes simplified handling during installation and replacement possible, permits defined and optimized cooling, satisfies a range of safety aspects, etc. Inside a module, component groups or submodules are in this case often formed from subsets of the multiplicity of power transistors.
In terms of the switching behavior of the power semiconductor arrangement, it is generally desirable for a current to be able to be switched on or off as rapidly as possible. Particularly in the case of voltage-controlled power transistors, in which a current can be switched between a first power electrode and a second power electrode by means of a control voltage applied between the first power electrode and a control electrode, this is made difficult by inductive effects, among other things. These inductive effects affect not only the control voltage and cause a deviation of the effective control voltage from the specified control voltage, but also affect the load current output and load current input.
For instance, an inductive influence furthermore takes place as a result of temporally varying currents through the rest of the power transistors on account of so-called mutual inductances. In current-carrying conductors, that is to say around the load current terminals as well, magnetic fields are also formed. The electrical current flowing in the terminals leads to the formation of a magnetic flux. The way in which these magnetic fields propagate in the space around the current-carrying conductors and how large the magnetic flux resulting therefrom is depends on the magnetic properties of the surroundings. In this case, not only the magnetic properties of the materials in the surroundings but also the presence of further magnetic fields, caused by other load current terminals, play a crucial role. By connecting at least two power semiconductor switching elements in parallel, the individual load-current-carrying paths are influenced magnetically in such a way that the inductances of said paths can differ greatly. This leads to an uneven current distribution, also referred to as an asymmetrical current distribution, in particular during the switching instant, with the result that the switching behavior of the entire power semiconductor arrangement is influenced thereby.
It has been found that it is possible to address the problem of current asymmetry by means of the manner in which power semiconductor switching elements are contact-connected, by virtue of the fact that the inductances can be “balanced” and the current asymmetry during switching of the power semiconductor switching elements can be largely eliminated, for example, by way of different geometric design of the connection tongues and/or by way of separate shieldings of one of more power semiconductor switching elements.
However, it has also been found that the so-called skin effect leads to an uneven current distribution, in particular, in the case of high-frequency current components during the switching process, since the high-frequency current components propagate close to surfaces and, in particular, close to edges. In the case of a plurality of power semiconductor switching elements contact-connected by means of a common connection plate per load current direction, this leads to outer power semiconductor switching elements having a higher resulting commutation inductance and inner power semiconductor switching elements having a lower resulting commutation inductance.